Date: Wed, 14 Mar 2001 22:06:31 -0800 (PST) From: Matt Dillon <dillon@earth.backplane.com> To: Garance A Drosihn <drosih@rpi.edu> Cc: "David O'Brien" <TrimYourCc@NUXI.com>, Brooks Davis <brooks@one-eyed-alien.net>, freebsd-arch@FreeBSD.ORG Subject: Re: [PATCH] add a SITE MD5 command to ftpd Message-ID: <200103150606.f2F66Vj38988@earth.backplane.com> References: <20010314084651.A23104@ringworld.oblivion.bg> <200103142342.QAA09233@usr08.primenet.com> <20010314161555.A4984@Odin.AC.HMC.Edu> <20010314185026.C7683@dragon.nuxi.com> <200103150256.f2F2u1b37896@earth.backplane.com> <p0501040ab6d5f1cb0b56@[128.113.24.47]>
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:If you're going to download it anyway, then there is zero point
:to doing the MD5. The way I'm reading this option, the ONLY
:reason to do an MD5 is to try and *-AVOID-* doing a download.
:That is all I want it for, at least.
I'm just trying to think of the situations where a user would do
this on a regular basis, and I simply can't imagine that
'unnecessary downloads' would account for then a few percent of
all the downloads made from a site. Or even 1%.
As far as checking to see if a file has changed or not... insofar
as any great use of ftp for synchronizing file trees the
modification time and file size has been used for ages and has
proven to work extremely well. MD5'ing isn't going to have any great
effect on reducing bandwidth verses simply looking at the modification
time and file size.
I see no point in adding a command that has so little effect on the
site's bandwidth useage, provides no significant enhancement of
operations OR security, and is yet another thing for the site
administrator to have to worry about in regards to abuse. Your
comment about checking to see if a file has changed is a case in point..
someone could very easily use the feature to check whole directory
trees for changes with insignificant impact on them, but a huge impact
on the server if it doesn't cache the MD5's somewhere. A single user
MD5ing hundreds of files would have a monsterous impact on an FTP
server.
On FTP servers, ls -lR is often disabled due to abuse. Many ftp
servers still leave it disabled. Most large ftp respositories now
run ls -lR as a cron job and store the results in an easily
downloadable file precisely because of the abuse that occurs when
users run ls -lR's.
Frankly, I see no redeeming value for a SITE MD5 command. It would be
a whole lot easier for a site administrator to simply generate MD5
lists nightly and store them in files on the ftp server itself for
users to download, just like many do for ls -lR. And it doesn't require
adding another command to the FTP server to make it work either.
-Matt
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